Simple DNS question - Unix

This is a discussion on Simple DNS question - Unix ; I am reading "Essential System Administration 3rd edition" (2002). The following has me a little confused: "Reverse lookup zones are assigned names of the form c.b.a.in- addr.arpa where c, b, and a are the third, second, and first components of ...

+ Reply to Thread
Results 1 to 3 of 3

Thread: Simple DNS question

  1. Simple DNS question

    I am reading "Essential System Administration 3rd edition" (2002). The
    following has me a little confused:

    "Reverse lookup zones are assigned names of the form c.b.a.in-
    addr.arpa where c, b, and a are the third, second, and first
    components of local network address, respectively. For example,
    10.168.192.in-addr.arpa is the reverse lookup zone for the 192.168.10
    subnet."

    Okay, just to clear first compent a = 192, second component b = 168,
    and third component c = 10; correct? Continuing on:

    "The order of numbers within the network address is reversed in the
    reverse lookup zone name. The first component, c, is omitted when it
    is not used for the network part of IP addresses: e.g., 1.10.in-
    addr.arpa is the reverse lookup zone for the 10.1 subnet."

    How is "c" the first compent? How is "c" the ommitted first component?
    If c = 10, then it is *not* ommited in the example given. From the
    example given, it looks to me like a and b are being ommited.

    I am not sure where the "1" comes from. I assume the full host address
    is 192.168.10.1. Or maybe the author is using a different network
    address and not telling anybody?

    My understanding is: in the address 192.168.10.1 - the 192.168.10 is
    the *network* part. So, in the example given, c *is* used in the
    network part.

    Is the author wrong, or am I just not understanding this?

  2. Re: Simple DNS question

    In article
    <22d3fc1d-05de-4073-bed7-7b77540ad24d@e6g2000prf.googlegroups.com>,
    walterbyrd wrote:

    > I am reading "Essential System Administration 3rd edition" (2002). The
    > following has me a little confused:
    >
    > "Reverse lookup zones are assigned names of the form c.b.a.in-
    > addr.arpa where c, b, and a are the third, second, and first
    > components of local network address, respectively. For example,
    > 10.168.192.in-addr.arpa is the reverse lookup zone for the 192.168.10
    > subnet."
    >
    > Okay, just to clear first compent a = 192, second component b = 168,
    > and third component c = 10; correct? Continuing on:
    >
    > "The order of numbers within the network address is reversed in the
    > reverse lookup zone name. The first component, c, is omitted when it
    > is not used for the network part of IP addresses: e.g., 1.10.in-
    > addr.arpa is the reverse lookup zone for the 10.1 subnet."
    >
    > How is "c" the first compent? How is "c" the ommitted first component?
    > If c = 10, then it is *not* ommited in the example given. From the
    > example given, it looks to me like a and b are being ommited.
    >
    > I am not sure where the "1" comes from. I assume the full host address
    > is 192.168.10.1. Or maybe the author is using a different network
    > address and not telling anybody?
    >
    > My understanding is: in the address 192.168.10.1 - the 192.168.10 is
    > the *network* part. So, in the example given, c *is* used in the
    > network part.
    >
    > Is the author wrong, or am I just not understanding this?


    The second paragraph you quoted is not talking about the 192.168.10
    subnet, it's talking about the 10.1 subnet, e.g. addresses like
    10.1.22.33, 10.1.100.30, 10.1.244.9, etc.

    And when they said "first component", they were referring to the
    reversed form, c.b.a.in-addr.arpa. c is first there. If you decide to
    put all your 10.1 reverse DNS entries into a single file, there's no c,
    just b.a.in-addr.arpa.

    --
    Barry Margolin, barmar@alum.mit.edu
    Arlington, MA
    *** PLEASE don't copy me on replies, I'll read them in the group ***

  3. Re: Simple DNS question

    In our last episode, the evil Dr. Lacto had captured our hero,
    walterbyrd , who said:
    >I am reading "Essential System Administration 3rd edition" (2002). The
    >following has me a little confused:
    >
    >"Reverse lookup zones are assigned names of the form c.b.a.in-
    >addr.arpa where c, b, and a are the third, second, and first
    >components of local network address, respectively. For example,
    >10.168.192.in-addr.arpa is the reverse lookup zone for the 192.168.10
    >subnet."


    So far so good.

    >"The order of numbers within the network address is reversed in the
    >reverse lookup zone name. The first component, c, is omitted when it
    >is not used for the network part of IP addresses: e.g., 1.10.in-
    >addr.arpa is the reverse lookup zone for the 10.1 subnet."


    The example shown in this paragraph is, in no way, related to the example
    shown in the previous paragraph.

    --hymie! http://lactose.homelinux.net/~hymie hymie@lactose.homelinux.net
    ------------------------ Without caffeine for 492 days ------------------------

+ Reply to Thread